The present invention relates to an apparatus and to a process for continuous or discontinuous production of sandwich composite elements, in particular metal/foam composite elements.
For the purposes of the present invention, “sandwich composite element” means a composite element composed at least of two facings and a core layer located between the facings. In particular, metal/foam composite elements are made up of at least of two metal facings and a core layer of foam, e.g. a rigid polyurethane (PU) foam. Such metal/foam composite elements having metal facings and a core layer of rigid polyurethane foam are known from the prior art and are sometimes referred to as metal composite elements. Additional layers may be provided between the core layer and the facings. For example, the facings may be finished, e.g., with a coating.
Possible uses for such metal composite elements are, for instance, plane or lined wall elements and profiled roof elements for industrial hall and cold storage construction. The metal composite elements may also be used as truck bodies, hall doors and gates and in container construction.
Production of these metal composite elements using a continuous or discontinuous process is known from the prior art. Apparatus for continuous production are disclosed, for example, in DE 1 609 668 A and DE 1 247 612 A.
In addition, it is known in the production of metal composite elements that application of a chemical component such as an adhesion promoter, bonding agent, resin or the like to the facings before the core layer is foamed in place improves adhesion of the foam to the metal facings. For example, the use of polymerization adhesives is described in DE 1 176 834 A. For the purposes of the present invention, such chemical components used to improve the adhesion of the core layer to the facings, are designated simply as adhesion promoters.
In addition to inadequate adhesion of the core layer to the facings, another problem encountered with metal/foam composites is encountered in the boundary areas of the foam core layer near the facings where defects arise in the foam, in general in the form of bubbles or altered cell structures. These defects in the foam may restrict the usability of the metal composite elements and are therefore undesirable. However, they may be reduced or wholly prevented by applying an adhesion promoter to the facings.
Conventionally, such adhesion promoters are applied to the facings by spraying or sprinkling by means of nozzles, drip strips, rakes or the like or spreading by means of large or small brushes, rollers or the like.
The known methods for applying the adhesion promoter are sometimes comparatively complex and/or result in uneven application of the adhesion promoter. In addition, considerable aerosol formation is associated with spray application of the adhesion promoter, leading to the loss of certain quantities of the adhesion promoter, since not all of the sprayed adhesion promoter lands on the facings but is released into the surrounding area instead. Additionally, emission of the spray mist into the surrounding area has to be prevented by complex extraction apparatuses. Depending on the type of adhesion promoter, blockage of the extraction apparatus may occur.